Sideways moving platforms isn't really a bad idea. They pulled it off in Duke3D by just forcing the platform to remain within its original sector. I took heavy advantage of this effect in my level designs by making massive vehicles that moved through a level, circular columns that would crush you if you touched them, and platforms you toggled on one end then rode across to another.
The only trouble is that SRB2, just like Doom, runs off of BSP trees, right? Duke3D does not. In a 2D BSP tree you can't really make a sector move back and forth without doing some serious dynamic calculations that I don't think the Doom BSP processor was ever designed to handle...
*shrugs* Ok, scratch the moving platform/sector idea, unless you want to rebuild SRB2 to not use BSP trees... which is an idea so lame I'll probably be hunted down and killed just for sarcastically mentioning it! *runs*
--- Gemini